1. Field of the Invention
This invention relates generally to batteries, and more particularly to temperature-dependent charging of batteries.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Examples of portable information handling systems include notebook computers. These portable electronic devices are typically powered by battery systems such as lithium ion (“Li-ion”) or nickel metal hydride (“NiMH”) battery packs including one or more rechargeable batteries. FIG. 1 shows a battery system 120 of a portable information handling system 100 having battery charge terminals 122, 124 that are temporarily coupled to corresponding charge output terminals 115, 116 of a battery charging apparatus 110. As so configured, battery charging apparatus 110 is coupled to receive current from current supply terminals 112, 114 (e.g., alternating current, or direct current from an AC adapter) and to provide DC charging current to battery charge terminals 122, 124 of battery system 120 via charge output terminals 115, 116. As shown, battery system 120 also includes battery system data bus (SMBus) terminals 126, 128 for providing battery state information, such as battery voltage, to corresponding battery charging apparatus data bus terminals 117, 118.
FIG. 2 shows a conventional lithium ion battery system 120 having a battery management unit (“BMU”) 202 responsible for monitoring battery system operation and for controlling battery system charge and discharge circuitry 270 that is present to charge and discharge one or more battery cells of the battery system. As shown, BMU 202 includes analog front end (“AFE”) 206 and microcontroller 204. Charge and discharge circuitry 270 of battery system 120 includes two field effect transistors (“FETs”) 214 and 216 coupled in series between battery charge terminal 112 and battery cell/s 224. FET 214 is a charge FET (“C-FET”) switching element that forms a part of charge circuit 260 that is controlled by microcontroller 204 and/or AFE 206 of BMU 202 using switch 218 to allow or disallow charging current to the lithium ion battery cell/s 224, and FET 216 is a discharge FET (“D-FET”) switching element that forms a part of discharge circuit 262 coupled in series with charge circuit 260 that is controlled by microcontroller 204 and/or AFE 206 of BMU 202 using switch 220 to allow or disallow discharge current from the battery cell/s 224. As shown, parasitic diodes are present across the source and drain of each FET switching element, i.e., to conduct charging current to the battery cell/s when the discharge FET switching element 216 is open, and to conduct discharging current from the battery cell/s when the charge FET switching element 214 is open.
During normal battery pack operations both charge and discharge FET switching elements 214 and 216 are placed in the closed state by respective switches 218 and 220, and AFE 206 monitors voltage of battery cell/s 224. If AFE 206 detects a battery over-voltage condition, BMU 202 opens the charge FET switching element 214 to prevent further charging of the battery cell/s until the over-voltage condition is no longer present. Similarly, if AFE 206 detects a battery under-voltage (or over-discharge) condition, BMU 202 opens the discharge FET switching element 216 to prevent further discharging of the battery cell/s until the under-voltage condition is no longer present. BMU 202 may also open the charge FET switching element 214 when the battery pack is in sleep mode.
A current sense resistor 212 is present in the battery pack circuitry to allow AFE 206 to monitor charging current to the battery cell/s. If the charge FET switching element 214 is supposed to be open (e.g., during sleep mode or battery over-voltage condition) but charging current is detected, BMU 202 permanently disables the battery pack by blowing an inline fuse 222 present in the battery circuitry to open the battery pack circuitry and prevent further over-charging. A thermistor 211 is present in the battery pack circuitry to allow AFE 206 to sense temperature of battery cell/s 224 for purposes of shutting down charging operations when temperature of battery cell/s 224 either exceeds a maximum allowable charging temperature or drops below a minimum allowable charging temperature.
FIG. 3 shows a battery charging apparatus 110 coupled to a conventional smart battery system 120 for a notebook computer. As shown, charging apparatus 110 includes charger circuitry 304 that is coupled to receive current from current supply terminals 112, 114, and to provide DC charging current to battery charge terminals 122, 124 of battery system 120 via charge output terminals 115, 116. Also shown is notebook computer system load 330 that is coupled to receive power from battery system 120 via coupled terminals 122 and 115. Charger circuitry includes charger regulation circuitry such as an analog controller with some digital functionality, and is configured to communicate with BMU 202 and/or through system BIOS of the notebook computer. BMU 202 controls battery system charge and discharge circuitry 270 based on system operating conditions. As shown in FIG. 3, battery system 120 includes SMBus terminals 126, 128 for providing battery state information, such as battery voltage and current, via battery charging apparatus data bus terminals 117, 118 to system embedded controller/keyboard controller (EC/KBC) 331.
Battery life (discharge time) is one important performance factor for users of notebook computers, and user dissatisfaction often results from shortened battery life. Shortened battery life typically becomes an increasingly significant problem as battery capacity degrades over multiple charge/discharge cycles. Many conventional notebook computer systems use Constant Current-Constant Voltage (CC-CV) charging mechanisms, where the constant current (CC) and constant voltage (CV) values are pre-determined.
Ambient temperature plays a role in battery capacity degradation, which is greater at higher and lower ambient temperatures than under normal room temperature ambient conditions. In particular, new battery capacity degradation is much more severe in cold environments than in room temperature or hot ambient temperature environments, and this effect may be seen in battery charge/discharge life cycle testing. Due to this effect of higher battery capacity degradation, much greater battery capacity degradation is tolerated by battery manufacturers and notebook computer manufacturers at cold ambient temperatures than at normal ambient temperatures. However, despite meeting battery specifications at cold ambient temperatures, notebook computer users find such a large reduction in battery capacity inconvenient.